Electroluminescent devices (hereinafter also referred to as EL devices) contain spaced electrodes separated by an electroluminescent medium that emits light in response to the application of an electrical potential difference across the electrodes. Through intensive investigations and a series of recent inventions organic electroluminescent devices of improved characteristics, both in terms of fabrication feasibility and operating performance have been developed.
In current preferred forms organic EL devices are comprised of an anode, an organic hole injecting and transporting zone in contact with the anode, an electron injecting and transporting zone forming a junction with the organic hole injecting and transporting zone, and a cathode in contact with the electron injecting and transporting zone. When an electrical potential is placed across the electrodes, holes and electrons are injected into the organic zones from the anode and cathode, respectively. Light emission results from hole-electron recombination within the device.
A class of organic EL devices that have exhibited highly desirable levels of efficiency and stability are those that have employed a metal oxinoid charge accepting compound to form the electron injecting and transporting zone of the organic EL device. Preferred metal oxinoid compounds have been identified as those that satisfy the formula: ##STR1## where
Me represents a metal,
n is an integer of from 1 to 3, and
Z represents the atoms necessary to complete an oxine nucleus.
R-1. VanSlyke et al U.S. Pat. No. 4,539,507 discloses in column 9, lines 14 to 16 inclusive, metal complexes of 8-hydroxyquinoline, where the metal is Zn, Al, Mg, or Li. In Example 9 the metal complex is bis(8-hydroxyquinolino)aluminum and in Example 10, bis(8-hydroxyquinolino)magnesium.
R-2. Tang et al U.S. Pat. No. 4,769,292 discloses constructing an organic EL device in which the luminescent layer is comprised of a charge accepting host material and a fluorescent material. The host material can be chosen from among diarylbutadienes, stilbenes, optical brighteners, and metal oxinoid compounds, with the following being listed among preferred embodiments: aluminum trisoxine, magnesium bisoxine, bis[benzo{f}-8-quinolino]zinc, bis(2-methyl-8-quinolinato)aluminum oxide, indium trisoxine, aluminum tris(5-methyloxine), lithium oxine, gallium trisoxine, calcium bis(5-chlorooxine), poly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane, dilithium epindolidione, 1,4-diphenylbutadiene, 1,1,4,4-tetraphenylbutadiene, 4,4'-bis[5,7-di(t-pentyl-2-benzoxazolyl]stilbene, 2,5-bis[5,7-di(t-pentyl-2-benzoxaolyl]thiophene, 2,2'-(1,4-phenylene-divinylene)bisbenzothiazole, 4,4'-(2,2'-bisthiazolylbiphenyl, 2,5-bis[5-.alpha.,.alpha.-dimethylbenzyl)-2-benzoxazolyl]thiophene, 2,5-bis[5,7-di(t-pentyl)-2-benzoxazolyl]-3,4-diphenylthiophene, and trans-stilbene.
R-3. VanSlyke et al U.S. Pat. No. 4,720,432 discloses organic EL devices in which the organic hole injecting and transporting zone is comprised of a layer in contact with the anode containing a hole injecting porphyrinic compound and a layer containing a hole transporting aromatic tertiary amine interposed between the hole injecting layer and the electron injecting and transporting zone. The metal oxinoid charge accepting compounds are those disclosed to form the electron injecting and transporting zone in R-2.
R-4. Tang et al U.S. Pat. No. 4,885,211 discloses organic EL devices with improved cathodes containing a metal oxinoid compound in the electron injecting and transporting zone. The metal oxinoid charge accepting compounds are those disclosed to form the electron injecting and transporting zone in R-2.
R-5. Perry et al U.S. Pat. No. 4,950,950 discloses organic EL devices in which the hole injecting and transporting zone is comprised of (a) a layer in contact with the anode containing a hole injecting porphyrinic compounds and (b) a layer containing a hole transporting silazane interposed between the hole injecting layer and the electron injecting and transporting zone. The metal oxinoid charge accepting compounds are those disclosed to form the electron injecting and transporting zone in R-2. Aluminum oxinate is set out in the Examples.
R-6. Kushi et al, "The Crystal and Molecular Structure of Bis(2-methyl-8-quinolinolato)aluminum(III)-.mu.-oxo-bis(2-methyl-8-quinoli nolato)aluminum(III)", J. Amer. Chem. Soc., 92(1), pp.91-96 (1970), discloses the preparation of the title and similar compounds.